Thursday, July 24, 2025
Safety Message – Maintenance of train detection systems
In the last three years more than 30 incidents involving failures of train detection systems, have been reported to ONRSR. These incidents have included short warnings at level crossings, non-operation of level crossing equipment, derailments, and other signalling issues such as wrong side failures.
In this safety message, we examine how poor wheel-rail interfaces caused by contamination and inadequate maintenance pose a risk to rail safety. The information covers:
- what train detection systems are and how they work
- the causes and contributing factors, to problems with train detection system reliability
- the controls that can minimise the risk.
What are train detection systems and how do they work?
Train detection systems track the safe movement of rolling stock.
Depending on the type, train detection systems work by using either an electrical current, an inductive/magnetic field or an optical beam of light. When a train passes over the railway tracks, the wheels of the train ‘shorts’ the electrical circuit, or activates or blocks the inductive/magnetic fields, or the optical beams of light, enabling the system to detect the presence of a train.
Rail contamination and/or poor maintenance interferes with these processes and the ability to accurately detect a train.
Causes and contributing factors
What are common causes of track contamination?
Three common causes of track contamination are:
- Railhead contamination: can be caused by rust, vegetation, chemicals, insects, grain, grease, oil, mud, excessive sand from rolling stock traction/braking systems, or protective paints and other contaminants on newly installed rail (e.g. recycled rail).
- Wheel contamination: includes tread corrosion, tread glazing from composition brake blocks or degraded wheel-to-rail contact profile. This can result in rolling stock wheels not making adequate contact with the rails.
- Type of rolling stock: trains with fewer axles tend to have poorer electrical conductivity, especially on rail with light contamination such as rust.
How does inadequate monitoring and maintenance cause rail safety incidents?
Examples of inadequate monitoring and maintenance include:
- inadequate calibration, adjustment, positioning or fixing of train detection system components e.g. incorrect calibration and certification of axle counter wheel counting sensors
- inadequate inspection, testing, reinstallation and certification of track detection systems e.g. not undertaken in accordance with the rail infrastructure manager and/or manufacturer’s specifications or safety related application conditions
- failure to identify high risk locations for contamination and implement appropriate controls
- failure to identify increased or decreased ballast resistance due to improved or deteriorated track ballast condition
- failure to identify deteriorated performance of track detection system components
- failure to identify damage to train detection systems due to environmental conditions such as inclement weather.
Controls
Operators must consider a range of factors, including the likelihood and the degree of harm, to determine what controls are reasonably practicable to implement – see the ONRSR Guideline – Meaning of duty to ensure safety so far as is reasonably practicable SFAIRP for more information.
While not an exhaustive list, ONRSR is aware of the following controls that are available and have been used in railways both in Australia and overseas. It should be noted that there are safety and operational benefits and detriments associated with each control.
Optimal Train Detection Systems
To reduce the likelihood of points moving while being traversed by rail traffic, operators should consider:
- Axle counters: in lieu of track circuits for train detection, where rail contamination or wheel-rail contact is an issue.
- High voltage impulse (HVI) track circuits: use a high voltage waveform which overcomes film resistance such as from light rust and general contamination. Historically, HVI track circuits provide improved wheel-to-rail shunt characteristics.
- Treadles and axle counters: can be used as a shunt assist (to assist train detection), as an overlay or primary detection system. The use of treadles or axle counters in any of these applications can assist in improving train detection. While treadles can enable reliable train detection if managed appropriately, please note that:
- treadles are generally used as a shunt assist aid and should not be used as a primary train detection device
- the application and use of any train detection system needs to be adequately and appropriately risk assessed.
Rail infrastructure controls
- Remote monitoring: allows for immediate notification of system changes and potential train detection system issues enabling prompt responses and quick rectification to ensure network safety.
- Trap track or track sequencing: a design characteristic of level crossing controls which keeps the level crossing operating despite a loss of track circuit shunt.
- Level crossing predictor settings: ‘motion detect’ or ‘loss of shunt’ settings can be adjusted or changed to a ‘positive start’ setting to ensure safe level crossing operation in the event of a momentary loss of track shunt.
- Slow-to-pick relays: these relays are designed to remain in the de-energised position for a short time despite voltage being applied to the controlling coils. They are typically used in conjunction with track circuits to remedy a brief reduction in train shunt characteristics during track circuit occupancy.
- Stainless-steel strips: welded onto the rail head within the approach sections of a level crossing or over points to prevent build-up of rust contamination on the rail surface.
- Rail scrubbing and rail milling activities: scrubbing and milling removes rust, scale and other contaminants from the rail head maintaining adequate contact between the wheel and rail.
- Protective mats: prevent contamination during adjacent works such as vegetation removal which can cause rail contamination.
- Checking and testing: performed by qualified and competent staff and undertaken in accordance with defined standards, procedures and technical maintenance plan service schedules. Examples of checking and testing include:
- checking axle counter or treadle operation, fixings, position in relation to rail, and calibration
- checking and testing of track circuits to ensure all components are in the applicable serviceable condition including:
- routine inspection of track ballast condition, insulated rail joints, and track circuit and traction bonding
- routine testing and calibration of track circuits to ensure values are in accordance with manufacturer and RIM specifications
- regular calibration and ‘train shunt’ checks and tests.
Rolling stock controls
- Testing existing, new or modified rolling stock: to ensure the integrity of on-board /on-train equipment and systems e.g. traction systems, (track circuit assistors, ATP equipment, wheel profiles. This can ensure rolling stock:
- reliably operates signalling train detection systems
- operates in accordance with all technical specifications
- does not cause any adverse impact on train detection systems
- Tread corrosion: ensuring wheels are free of tread corrosion, tread glazing from composition brake blocks or degraded wheel-to-rail contact profiles (see ONRSR Safety Message – Sticking brakes and Technical Review: Wheel Failure Incidents and Other Data in the Hunter Valley: 2013–2015)
- Worn wheels or flanges: worn wheels or flanges can cause wheel detection issues which can impact the reliable operation of axle counter systems.
- TCA: installed on board rolling stock and can improve the shunting characteristics of the track and operation of a track circuit by increasing the effective track circuit voltage. Ensure TCA devices, where fitted, are correctly connected and functioning in accordance with all applicable design and technical specifications.
- Sanding and de-sanding systems: ensure that sanding systems are functional and delivering the correct quantities of sand. For de-sanding systems ensure such systems are functional.
Overall management
- Patrols and monitoring: regular track patrols to identify rail head contamination and monitoring of train detection systems.
- Investigation and rectification: to reduce the potential for reoccurrences, promptly investigate the causes of train detection system faults and defects e.g. with points, switches or level crossings. Rectify identified faults and defects which can include monitoring as part of ongoing asset management processes.
- Intervention levels: ensure systems, procedures and standards define intervention points when the above actions need to take place. Key aspects to consider include:
- minimum number of train movements during a set period
- rail condition
- train type and tonnage
- weather and environmental conditions
- location and susceptibility to contaminants
- age and condition of equipment or system.
- Traffic management: manage train movements to ensure trains regularly traverse all areas of the network where train detection systems are installed. Additionally, following periods where rail traffic has been absent, ensure appropriate system safety integrity certification testing is undertaken.
- Registers: maintain a register, database or system to capture and record high priority and high-risk locations, including when the above actions and activities have taken place.
Safeworking and training
- Book out equipment: book out and disconnect faulty equipment and/or install alternative manual safeworking protection in accordance with network rules. Signalling equipment affected by train detection faults that could be booked out includes:
- track circuits
- points
- signal routes
- level crossing equipment.
- Network control and driver circulars: provide a formal notice to train drivers and network controllers/signallers as a reminder and ensure consistent understanding and application to note changes to the operation of the rail network.
- Network controller/signaller training and auditing:
- scenario-based training and positive mentorship help network controllers/signallers appropriately manage train movements in specific situations such as recognising wrong side signalling faults and loss of train detection indications.
- structured, practical, competency-based training for rail infrastructure workers covering:
- monitoring, calibration and testing of train detection systems
- recognition and management contaminated rail
- applicable, regular and timely refresher training and mentorship
- regular on the job task-based audit/assessment
- ongoing documented practical formal/informal skill and competency training, mentorship and assessment.
Key documents and actions
The controls listed in this safety message are not applicable to every operator. Where they are not applicable, operators should document the reasons in a risk register or risk assessment to demonstrate compliance with section 100 of the Rail Safety National Law. If the controls listed here are applicable, operators need to comply with their Management of Change processes – see ONRSR Safety Message – Management of Change.
Guidance material that can assist includes: